This invention provides new fast-curing liquid adhesives for laminating and sealant purposes.
Known adhesive compositions which cure in the presence of free-radical catalysts, often called vinyl-polymerizable sealants, are generally based on syrupy solutions containing various olefinically unsaturated monomers and various compatible polymers. Thus, for example, U.S. Pat. No. 3,333,025 discloses compositions comprising monomeric styrene and methyl methacrylate and their partially polymerized copolymers in the presence of polychloroprene and optionally up to 5% acrylic acid. U.S. Pat. No. 3,725,504 discloses similar compositions containing also acrylate polymers such as interpolymers of methyl methacrylate and ethyl acrylate, and containing about 8 to 12% of monomeric methacrylic acid. Compositions such as these are cured through the catalytic agency of a free-radical donor such a benzoyl peroxide or azobisisobutyronitrile.
In commercial application of such adhesive systems, there is an ever-increasing demand for rapid cure, i.e. there is a requirement for short "cure time", defined as the duration of time between the time of contacting the composition with catalyst and the time when the assembly bearing the adhesive can be easily handled without causing relative movement of the joined parts.
Formulations of the prior art commonly provide "cure times" of around a half-hour. More quickly curing variations can be made which become set in about ten minutes or in some cases even as quickly as about five minutes, but this is often at the expense of other desirable properties such as flexibility, toughness, adhesive bonding strength or storage stability of the uncatalyzed composition. Furthermore, in the design of many commercial operations, there is now a trend toward even shorter cure-times, of the order of one minute.
The new adhesives of this present invention contain substantial amounts of tris(dimethylaminomethyl)phenol. To the best knowledge of the inventor, there has been no prior disclosure of any composition containing acrylate or related ethylenically unsaturated monomers together with tris(dimethylaminomethyl)phenol. Perhaps one of the reasons for this is that other phenolic derivatives such as, for example, hydroquinone and catechol are known to be inhibitors of free-radical polymerization of olefinically unsaturated monomers even when present in relatively small amounts.